Aerodynamic Performance and Wake Flow of Crosswind Kite Power Systems

Abstract

This paper presents some results from a computational fluid dynamics (CFD) model of a multi-megawatt crosswind kite spinning on a circular path in a straight downwind configuration. The unsteady Reynolds averaged Navier-Stokes equations closed by the k−ω SST turbulence model are solved in the three-dimensional space using ANSYS Fluent. The flow behaviour is examined at the rotation plane, and the overall (or global) induction factor is obtained by getting the weighted average of induction factors on multiple annuli over the swept area. The wake flow behaviour is also discussed in some details using velocity and pressure contour plots. In addition to the CFD model, an analytical model for calculating the average flow velocity and radii of the annular wake downstream of the kite is developed. The model is formulated based on the widely-used Jensen’s model which was developed for conventional wind turbines, and thus has a simple form. Expressions for the dimensionless wake flow velocity and wake radii are obtained by assuming self-similarity of flow velocity and linear wake expansion. Comparisons are made between numerical results from the analytical model and those from the CFD simulation. The level of agreement was found to be reasonably good. Such computational and analytical models are indispensable for kite farm layout design and optimization, where aerodynamic interactions between kites should be considered.

Wing Deformation of an Airborne Wind Energy System in Crosswind Flight Using High-Fidelity Fluid–Structure Interaction

“…AWESs Aero S: [3,4] S: [5][6][7], U: [8] S: [9,10], U: [11,12] Structure [3] [6] [5,7,9] FSI [3,5,7] [6] [9,13] Atmosphere [12,14,15] [4] (LES), [12] (RANS) Dynamics [8] [4,16] [ 5,17] In Table 1, we review several levels of fidelity for different fields. In aerodynamics, lowfidelity models are based on the lifting-line techniques or look-up tables.…”

“…In [4], the dynamic motion of an AWE system was considered with the low-fidelity modeling of AWES aerodynamics using actuator methods and steady airfoil coefficients in a large-eddy simulation (LES) of wind. Kheiri et al [12] analyzes the wake flow of an AWE system using unsteady Reynolds-average Navier-Stokes (RANS) for both AWE system aerodynamics and wind simulation. Efforts were made by Kaufman-Martin et al [14] and Gaunaa et al [15] to develop low-cost models for AWE wake and induction.…”

Moving control surfaces in a geometry-resolved CFD model of an airborne wind energy system

“…However, that study focuses on a steady horizontal flight, where the crosswind motion was neglected and the control surfaces were set in at a fixed position. Keihri et al [3] focused on the wake flow of an AWES system using unsteady RANS for both the AWE system aerodynamics and wind simulation assuming circular flight motion. Hence, they considered only the main wing and neglected the control surfaces.…”